1. Field of the Invention
This invention relates to a coding equipment for converting a parallel digital signal into a serial digital signal.
2. Description of the Prior Art
It is commonly known that, in a centralized control of physical quantities such as voltage, current and temperature measured at remote points, these physical quantities are sampled with a suitable period at the individual measuring points, and after converting the respective sampled physical quantities into parallel digital signals by an analog-digital converter, these parallel digital signals are converted into a succession of serial digital signals to be transmitted to a central control station. In this case, in order that the information processing, storing and other operations in the central control station can be efficiently carried out, it is required that the information transmitted one after another in the form of the serial digital signal have the same number of bits regardless of the magnitude of the absolute value of the physical quantities sampled periodically. On the other hand, however, the fact that the information transmitted one after another in the form of the serial digital signal have the same number of bits means that the greatest value of each information is also limited to a predetermined number of bits even when great variations occur in the physical quantities. Thus, the magnitude of the physical quantity corresponding to the least significant digit (LSD) is inevitably increased resulting frequently in a great error when the physical quantity is small.
In an effort to obviate the above defect, a proposal is made in, for example, U.S. Pat. No. 3,298,016 in which the magnitude of a physical quantity is coded as a combination of a numerical value of a predetermined number of digits making possible to express the numerical value by a predetermined number of bits and an index representing the largeness of the numerical value. This proposal is effective from the standpoint that physical quantities are converted into signals of the same number of bits and can be coded with high precision. However, the means disclosed in this proposal cannot be utilized when a fully digital unit is desired due to the fact that means for handling an analog quantity is included therein.